In a bowl add the egg and sugar and whisk until sugar dissolves.
Add the vegetable oil and grate the zest of the lemon and mix again, to incorporate the ingredients together.
Add the flour and the baking powder and mix to combine, first with a spatula and then with your hands, once the dough has started to form, until you obtain the compact dough.
Split the dough into 12 pieces of the same size and roll them into balls.
Transfer each piece into a muffin mold, then press them with your fingers to cover the whole part of the muffin mold.
Prick the little tarts with a fork, and then bake at 360°F (180°C) for about 30 minutes.
In a saucepan, in the meantime, add the milk, vanilla sugar, cornstarch, sugar and egg yolk and mix until the cream starts forming and thicking.
Add the lemon juice and keep stirring over low heat.
Once the cream has reached the desired velvety texture, take it off the heat and let it cool down.
Transfer the various pastry baskets to the plate and fill each of them with the prepared lemon cream, using a spoon to dose it.
Decorate with a generous drizzle of powdered sugar.
